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Original question:

BQ32002: BQ32002D

BQ32002: Battery Draining Issue of RTC Coin Cell using BQ32002D

Mohit Saharan
Prodigy 80 points
Part Number: BQ32002


Tool/software:

Hi Team,

We are using BQ32002D RTC Clock chip in our design. Refer below Schematic for your reference and we are using CR2016 Coin cell Battery from Duracell and Panasonic. 

Schematic:

Observations:

1.) Connect the VCC = 3.3V, Vback = 3.1V, Observed Iback is 1.1uA continuous current. (Coin Cell was present before VCC) (OFF to ON Condition) (RTC Programmed) 

2.) Remove the VCC = 0V, Vback = 3.1V, Observed Iback is 1.3uA continuous current. (Coin Cell was present before VCC) (ON to Off Condition) (RTC Programmed) 

3.) Connect the VCC = 3.3V, Vback = 3.1V, Observed Iback is 0.66uA continuous current. (Coin Cell was connected once VCC is ON) (OFF to ON Condition) (RTC Programmed) 

4.) Connect the VCC = 3.3V, Vback = 3.1V, Observed Iback is 1.8uA  continuous current. (Coin Cell was connected once VCC is ON) (OFF to ON Condition) (RTC Not Programmed)

5.) Connect the VCC = 3.3V, Vback = 3.1V, Observed Iback is 1.05uA  continuous current. (Coin Cell was connected once VCC is ON) (OFF to ON Condition) (RTC Programmed)

Problem Statement:

Why RTC is consuming/draining current from Vback in presence of VCC in case of 1,3, 4, and 5 ?

  • 0
    TI__Guru** 110530 points

    Hi Mohit,

    I don't know, for example in configuration 1, the device should switch to use Vcc.

    How did you measure the current? What test equipment did you use?

  • 0 in reply to Noel Fung
    Prodigy 80 points

    Hi Noel,

    Thanks for the quick response.

    We are using a Joule Meter Part number :  JS110: Precision DC Energy Analyzer). We have removed R414 from Schematic and connected this Joule meter in series to measure the current. 

    One more observation we have as listed below:

    6.) Connect the VCC = 3.3V, Vback = 3.1V, Observed Iback is 1.05uA  continuous current and observed a peak of 60uA current. (Coin Cell was connected once VCC is ON) (ON to OFF Condition) (RTC Programmed)

  • 0 in reply to Mohit Saharan
    Prodigy 80 points

    Hi Team,

    Any update on this? 

  • 0 in reply to Mohit Saharan
    TI__Guru** 110530 points

    Hi Mohit,

    Given this is a very simple device, I don't know why there is Iback even if Vcc exist.

    couples of thing we can try:

    Can you remove R417 or connect R417 to VDD_3V3_RTC?

    Can you use other multimeter to measure Iback?

    Instead of measuring current, can you change R414 to, say 1Ω, and then measure the voltage across the resistor?